Differential Diagnosis for the Patient

The patient's presentation of syncope, dysarthria, right upper and lower extremity weakness, and facial weakness after scuba diving suggests a neurological insult likely related to the diving activity. Here's the differential diagnosis categorized for clarity:

• Single most likely diagnosis

  • Arterial gas embolism: This condition occurs when gas bubbles enter the arterial circulation, which can happen if a diver surfaces too quickly, allowing nitrogen bubbles to form in the bloodstream. The patient's rapid ascent and subsequent neurological symptoms make this the most plausible diagnosis. The symptoms of dysarthria, extremity weakness, and facial weakness are consistent with a cerebral arterial gas embolism.

• Other Likely diagnoses

  • Decompression sickness: Also known as the "bends," this condition occurs when gas bubbles form in the body due to rapid changes in pressure. While it often presents with joint pain, neurological symptoms can occur if the bubbles affect the spinal cord or brain. The patient's symptoms and history could fit this diagnosis, but the specific neurological deficits might be less common than in arterial gas embolism.
  • Immersion pulmonary edema: This condition involves fluid accumulation in the lungs due to diving, which can lead to respiratory distress. However, it might not directly explain the neurological symptoms unless hypoxia from pulmonary edema led to cerebral injury. It's less likely given the specific pattern of neurological deficits.

• Do Not Miss diagnoses

  • Pneumothorax: Although less directly related to the neurological symptoms, a pneumothorax could occur due to lung overexpansion during diving. If missed, it could lead to significant morbidity or mortality, especially if it progresses to a tension pneumothorax. The presentation might not directly correlate with the neurological findings, but it's a critical condition to rule out in a diver with respiratory or chest symptoms.
  • Nitrogen narcosis: This condition, caused by the anesthetic effect of nitrogen at depth, typically presents with altered mental status or loss of judgment but does not usually cause the specific neurological deficits seen in this patient after surfacing. However, it could contribute to unsafe behavior leading to other injuries.

• Rare diagnoses

  • Nitrogen narcosis (in the context of causing the patient's specific symptoms): While nitrogen narcosis can cause neurological symptoms, it's rare for it to present in this manner after surfacing and does not typically cause localized neurological deficits like those described.
  • Other rare conditions related to diving, such as marine envenomation or drowning, do not fit the patient's presentation as well as the listed diagnoses and would be considered only if other evidence supported these conditions.